To date, a background difference method is known as a method of detecting a moving object that appears as a foreground from a moving image captured by a camera. In the background difference method, a background image (also referred to as a background model) that does not include an object to be detected is detected from a moving image captured by a camera and is stored. The difference of the background image is obtained from a moving image captured by the camera so that an image area in which a moving object appears is detected.
As a technique for detecting a background image to be used for a background difference method, a technique is known that controls a pixel value of each area in a monitoring image using a predetermined transmittance ratio and updates the pixel value of the area corresponding to a background image in sequence. A technique is known that increases a count value for pixels other than the pixels determined to be in a moving object area and updates the background image data of the pixels having the count value that has reached a predetermined value. A technique is known that determines, as a still area, a portion having a still time that becomes equal to or higher that a predetermined threshold value for determining stillness by counting the number of continuous appearances as a foreground and creating a new background model of an area determined to be a still area.